[1/6] mm: make the vma list be doubly linked

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index f478e39..8a8a765 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -134,7 +134,7 @@  struct vm_area_struct {
 					   within vm_mm. */
 
 	/* linked list of VM areas per task, sorted by address */
-	struct vm_area_struct *vm_next;
+	struct vm_area_struct *vm_next, *vm_prev;
 
 	pgprot_t vm_page_prot;		/* Access permissions of this VMA. */
 	unsigned long vm_flags;		/* Flags, see mm.h. */
diff --git a/kernel/fork.c b/kernel/fork.c
index 7fbc5e3..49ffdad 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -301,7 +301,7 @@  out:
 #ifdef CONFIG_MMU
 static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 {
-	struct vm_area_struct *mpnt, *tmp, **pprev;
+	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 	struct rb_node **rb_link, *rb_parent;
 	int retval;
 	unsigned long charge;
@@ -329,6 +329,7 @@  static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 	if (retval)
 		goto out;
 
+	prev = NULL;
 	for (mpnt = oldmm->mmap; mpnt; mpnt = mpnt->vm_next) {
 		struct file *file;
 
@@ -360,7 +361,7 @@  static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			goto fail_nomem_anon_vma_fork;
 		tmp->vm_flags &= ~VM_LOCKED;
 		tmp->vm_mm = mm;
-		tmp->vm_next = NULL;
+		tmp->vm_next = tmp->vm_prev = NULL;
 		file = tmp->vm_file;
 		if (file) {
 			struct inode *inode = file->f_path.dentry->d_inode;
@@ -393,6 +394,8 @@  static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 		 */
 		*pprev = tmp;
 		pprev = &tmp->vm_next;
+		tmp->vm_prev = prev;
+		prev = tmp;
 
 		__vma_link_rb(mm, tmp, rb_link, rb_parent);
 		rb_link = &tmp->vm_rb.rb_right;
diff --git a/mm/mmap.c b/mm/mmap.c
index f487849..a8d1651 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -401,19 +401,26 @@  static inline void
 __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct vm_area_struct *prev, struct rb_node *rb_parent)
 {
+	struct vm_area_struct *next;
+
+	vma->vm_prev = prev;
+
 	if (vma->vm_flags & VM_EXEC)
 		arch_add_exec_range(mm, vma->vm_end);
 	if (prev) {
-		vma->vm_next = prev->vm_next;
+		next = prev->vm_next;
 		prev->vm_next = vma;
 	} else {
 		mm->mmap = vma;
 		if (rb_parent)
-			vma->vm_next = rb_entry(rb_parent,
+			next = rb_entry(rb_parent,
 					struct vm_area_struct, vm_rb);
 		else
-			vma->vm_next = NULL;
+			next = NULL;
 	}
+	vma->vm_next = next;
+	if (next)
+		next->vm_prev = vma;
 }
 
 void __vma_link_rb(struct mm_struct *mm, struct vm_area_struct *vma,
@@ -500,7 +507,11 @@  static inline void
 __vma_unlink(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct vm_area_struct *prev)
 {
-	prev->vm_next = vma->vm_next;
+	struct vm_area_struct *next = vma->vm_next;
+
+	prev->vm_next = next;
+	if (next)
+		next->vm_prev = prev;
 	rb_erase(&vma->vm_rb, &mm->mm_rb);
 	if (mm->mmap_cache == vma)
 		mm->mmap_cache = prev;
@@ -2013,6 +2024,7 @@  detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 	unsigned long addr;
 
 	insertion_point = (prev ? &prev->vm_next : &mm->mmap);
+	vma->vm_prev = NULL;
 	do {
 		rb_erase(&vma->vm_rb, &mm->mm_rb);
 		mm->map_count--;
@@ -2020,6 +2032,8 @@  detach_vmas_to_be_unmapped(struct mm_struct *mm, struct vm_area_struct *vma,
 		vma = vma->vm_next;
 	} while (vma && vma->vm_start < end);
 	*insertion_point = vma;
+	if (vma)
+		vma->vm_prev = prev;
 	tail_vma->vm_next = NULL;
 	if (mm->unmap_area == arch_unmap_area)
 		addr = prev ? prev->vm_end : mm->mmap_base;
diff --git a/mm/nommu.c b/mm/nommu.c
index b76f3ee..e48b38c 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -609,7 +609,7 @@  static void protect_vma(struct vm_area_struct *vma, unsigned long flags)
  */
 static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
 {
-	struct vm_area_struct *pvma, **pp;
+	struct vm_area_struct *pvma, **pp, *next;
 	struct address_space *mapping;
 	struct rb_node **p, *parent;
 
@@ -669,8 +669,11 @@  static void add_vma_to_mm(struct mm_struct *mm, struct vm_area_struct *vma)
 			break;
 	}
 
-	vma->vm_next = *pp;
+	next = *pp;
 	*pp = vma;
+	vma->vm_next = next;
+	if (next)
+		next->vm_prev = vma;
 }
 
 /*